Method for regulated injection of liquid carbon dioxide in a pressured liquid

ABSTRACT

Method and its associated device for the regulated injection of liquid carbon dioxide (CO 2     L   ) into a liquid (L) under pressure inside a chamber. The liquid carbon dioxide (CO 2     L   ) is, according to this method, injected at a fixed flow rate, in stepped mode, under the protection of a stream of gas (when injection is stopped).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject of the present invention is a method and a device for theregulated injection of liquid carbon dioxide (CO₂ _(L) ) into a liquidunder pressure. The regulation of the injection of the CO₂ _(L) is,according to the invention, set at a fixed flow rate, in stepped mode.

The method and device of the invention are quite particularly suitablefor injecting CO₂ _(L) into a liquid circulating under pressure througha pipe. The context of the present invention is that of the treatmentwith carbon dioxide (CO₂) of any type of pressurized liquid,particularly liquids consisting of reaction mediums, industrialeffluent, drinking water, etc. In the context of the said presentinvention, the Applicant proposes an optimized technique for theinjection of liquid carbon dioxide (CO₂ _(L) ), this being optimizedparticularly both from the point of view of protection from the liquidinto which the said CO₂ _(L) is injected and from the point of view ofenvironmental protection.

2. Description of the Related Art

In general, the injection of gaseous carbon dioxide (CO₂ _(G) ) is atechnique that has been fully mastered. However, implementation of thesaid technique assumes prior vaporization of the carbon dioxide storedin the liquid state:

Such prior vaporization presupposes that the user site comprises avaporizer and entails a not insignificant power consumption. To be ableto avoid such prior vaporization is obviously economically veryattractive, both as regards saving on investment (absence of avaporizer) and in terms of savings on running costs (absence of powerconsumption).

The—direct—injection of CO₂ _(L) , while being of undisputed economicalbenefit, does, however, prove to be a technique which is more difficultto implement. Those skilled in the art are not unaware of this fact.

The Applicant has already proposed a technique for the—direct—injectionof CO₂ _(L) . This technique is described in Patent ApplicationFR-A-2,641,854. It is relatively complicated and its implementationrequires substantial investment. Its implementation is in fact generallyonly justified in large installations if significant amounts of CO₂ _(L)are to be injected. The said technique involves, for injecting avariable flow rate of CO₂ _(L) (permanent and non-stepwise regulatedflow of CO₂ _(L) ), the injection being regulated in proportional mode:

a controlled valve, of the proportional type (with variable flow rate)with no injector;

an upstream-pressure regulator for delivering the CO₂ _(L) ;

and is necessarily implemented with a CO₂ pressure, between the saidvariable-flow rate valve and the said upstream-pressure regulator, whichis higher than the triple point pressure of CO₂ (a pressure higher than5.2 bar).

SUMMARY OF THE INVENTION

The Applicant has wished to develop another technique for the regulatedinjection of CO₂ _(L) into a liquid under pressure, which techniquewould, in particular, be easier to implement. It now proposes such analternative technique which is particularly well-suited (but notstrictly limited) to contexts in which the large investment needed toimplement the technique according to FR-A-2,641,854 is not economicallyviable. According to the said other technique now claimed, the CO₂ _(L)is injected at a fixed flow rate, in stepped mode (all or nothing). Theinjection is regulated, according to the invention, in a different waythan in FR-A-2,641,854. It may, in absolute terms, be considered ashaving poorer performance.

When implementing this type of injection of CO₂ _(L) the injection beingregulated to occur in stepped mode, it is necessary, each time theinjection of CO₂ _(L) stops, to be able to avoid:

any running of the pressurized liquid treated with the said CO₂ _(L)back into the device used for injecting the said CO₂ _(L) (this isliable to lead to the blocking of the injector with, for example, solidresidues contained in the said liquid); and

any formation of plugs of dry ice, particularly at the location of thesaid device for injecting the said CO₂ _(L) (cold).

Faced with this technical problem which is inherent to the stepwiseregulated injection of CO₂ _(L) into a pressurized liquid, the Applicantrecommends, each time the injection of the said CO₂ _(L) stops, theintervention of a gas. The said gas has the dual function of drivingback the pressurized treated liquid and of protecting (insulating) theinjection device (which thus remains operational) from the said treatedliquid which is liable to freeze in situ.

BRIEF DESCRIPTION OF THE FIGURE OF THE DRAWING

The FIGURE of the Drawing illustrates a device for carrying out oneembodiment of the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to its first subject, the invention therefore relates to anoriginal method for the regulated injection of liquid carbon dioxide(CO₂ _(L) ) into a liquid under pressure and more specifically to amethod for the regulated injection, at a fixed flow rate, in steppedmode, of CO₂ _(L) into a liquid under pressure implemented under theprotection of a stream of gas (when the said injection of CO₂ _(L) isstopped).

According to the said original method of the invention, the said CO₂_(L) is injected into the liquid under pressure inside a chamber underthe following conditions:

it is injected at a fixed flow rate, in stepped mode, by an injectiondevice comprising an injection valve and an injection head tapped into awall of the said chamber; the said injection head being positioneddirectly at the outlet from the said injection valve;

as soon as its injection stops each time, a gas is substituted for it:as soon as each injection of liquid carbon dioxide (CO₂ _(L) ) stops, agas is delivered into the said liquid through the said injection head inplace of the said liquid carbon dioxide (CO₂ _(L) ); the said gas beingdelivered at sufficient pressure to prevent any of the said liquid fromrunning back into the said injection head.

The injection of CO₂ _(L) according to the method of the invention istrue injection, direct injection into the liquid which is to be treated,through a wall of the chamber containing the said pressurized liquid. Toimplement it, the said injection involves an appropriate injectiondevice which comprises an injection valve and an injection head. Thesaid injection valve comprises a valve, for example of the ball valvetype, associated with an injector. The said injector is more or lessintegrated into the structure of the said valve. For good injection, theperson skilled in the art will readily understand firstly that theinjector must not be truly separate from the valve and secondly that theinjection head has to be positioned directly at the outlet from theinjection valve.

The regulated injection according to the invention is, as alreadymentioned, of the type of injection with a preset fixed flow rate, instepped mode. The injection valve is an all or nothing valve.

As soon as the said valve is closed, and CO₂ _(L) is no longer beinginjected, the gas characteristically comes into action. It intervenes,at the injection head (downstream of the injection valve) in place ofthe said CO₂ _(L) , to be delivered into the liquid under pressure. Itwill be readily understood that, according to an advantageousalternative form, the said injection head has at least two inlets:

one for the CO₂ _(L) ,

one for the protective gas; and one outlet for delivering, alternately,the said CO₂ _(L) and the said protective gas, into the pressurizedliquid.

In order to play its part as a gas that protects the injection devicefrom the pressurized liquid, the said gas is obviously used atsufficient pressure.

The said protective gas (providing, in particular, thermal protectionfrom the CO₂ _(L) injected at about −80° C.) which is characteristicallyinvolved in the implementation, according to the invention, of theinjection of C₂ _(L) in stepped mode into a liquid under pressure may,in particular, consist of a gas which is “inert” with respect to thesaid liquid, “compatible” with the said liquid and not likely toadversely affect it, or to react chemically with it (we are talking hereabout at least relative inertness). It may, in particular, be a gaswhich is inert not in the chemical meaning of the term (this then isabsolute inertness), and be an inert gas which is nitrogen (N₂).

The scope of the invention does not, however, in any way include theuse, by way of protective gas, of another type of gas, a gas which isnot inert. Thus, according to a particularly preferred alternative form,the said protective gas is not an inert gas but consists of carbondioxide: CO₂ _(G) . In this alternative form, the liquid under pressuretherefore receives CO₂ _(L) and CO₂ _(G) alternately. The said CO₂ _(G)may come from any suitable source. Advantageously it comes fromvaporizing a fraction of the CO₂ _(L) tapped from the CO₂ _(L) supplycircuit of the injection device upstream of the said injection device.Just one CO₂ _(L) supply source is therefore needed to implement thisadvantageous alternative form of the method of the invention. Conscioususe of some other non-inert gas may also be envisaged; the said gasthen, in addition to its primary function of acting as a protective gas,fulfilling at least one other function.

Whatever the nature of the gas delivered into the liquid under pressurewhen the injection of CO₂ _(L) stops—inert gas, CO₂ _(G) , other gas—itmay be sensible to remove the said gas, at least partially, from the aidliquid. Such removal cannot be harmful, if performed carefully, insofaras the said gas, simply by being delivered into the liquid, hasfulfilled its function of safeguarding the injection of CO₂ _(L) . Bycontrast, in certain contexts, it may prove to be highly beneficial oreven practically compulsory. It is possible, in particular, thus toprevent the creation of resulting layers or pockets of gas in thechamber containing the liquid under pressure.

If the said chamber consists of a pipe through which the said liquidunder pressure flows, under the action of a pump, the person skilled inthe art will readily understand that such pockets of gas are likely tocause the said pump to loose its prime. To constantly maintain a liquidcharge downstream of the said pump it is therefore strongly recommended,when implementing the method of the invention, that the gas deliveredinto the liquid be removed opportunely (when the said pump is stopped).

In general, the protective gas delivered when the injection of CO₂ _(L)is stopped, is therefore advantageously at least partially removed. Thegas thus recovered may advantageously be recycled (by way of protectivegas).

According to the method of the invention, the injection of CO₂ _(L) :

at a fixed flow rate, in stepped mode,

under the protection of a stream of gas, is generally implemented in thefollowing conditions: the CO₂ _(L) is injected at an upstream pressureof between about 14·10⁵ and 20·10⁵ Pa (14 and 20 bar) and at an upstreamtemperature of between −20° C. and −30° C.

Advantageously, for obvious safety reasons, the said injection of CO₂_(L) is carried out with control of the temperature of the liquid intowhich the said CO₂ _(L) is injected; the injection of the said CO₂ _(L)being stopped as soon as the temperature of the liquid is below areference temperature. This is because it is necessary to be able, atany moment, to avoid the consequences of an abnormal length of CO₂ _(L)injection period (particularly inherent in equipment failure; failure ofthe injection valve for example), so that at any moment to avoid adangerous drop in the temperature of the liquid which may lead to theicing-up (with dry ice) of the chamber containing the said liquid.

The method according to the invention, as described hereinabove ingeneral terms and as described hereinbelow more specifically withreference to the single appended figure, can be implemented in variouscontexts. As already mentioned, it is particularly well-suited to theregulated injection, in stepped mode, of CO₂ _(L) into a liquidcirculating under pressure through a pipe. Such a liquid may circulateat pressures up to 8-10 bar. It generally circulates at pressures from4-5 bar. In any event, the Applicant has been able to verify thefeasibility and advantages of its new reliable method for injecting CO₂_(L) into liquids circulating at such pressures.

According to the invention, the liquids “treated with CO₂ _(L) ” mayconsist of any sort of liquid: in particular, these may be reactionmediums, industrial effluent, drinking water, etc.

They may be treated with CO₂ _(L) for various purposes, particularly fordescaling purposes and/or for the purpose of preventing the build-up ofscale in the devices containing them or through which they circulate.

The method of the invention is also quite particularly well-suited tolowering and advantageously controlling the pH of industrial effluent,before disposing of it down the drain. In this context, the injection ofCO₂ _(L) is advantageously directly slaved to the measuring of the pH.

The second subject of the present invention, mainly a device for theregulated injection of liquid carbon dioxide (CO₂ _(L) ) into a liquidunder pressure inside a chamber, the device being suited to theimplementation of the method that was the first subject of the saidpresent invention, will now be described, in general terms.

The said device comprises:

an injection valve and an injection head tapped into a wall of the saidchamber, the said injection head being positioned directly at the outletof the said injection valve; the said injection valve 1 a beingconnected by a supply circuit to a suitable source S of liquid carbondioxide (CO₂ _(L) ) and being suitable for injection at a fixed flowrate in stepped mode; and

means for supplying the said injection head with a gas.

It in fact comprises suitable means for implementing an injection of CO₂_(L) at a fixed flow rate in stepped mode; the means being arranged toallow the protective gas to be delivered each time the said injection ofCO₂ _(L) stops. The said suitable means comprise the injectionvalve—valve+injector or valve incorporating the said injector—and aninjection head. In original manner, the said injection head according tothe invention can be supplied with CO₂ _(L) and with gas alternately fordelivering the said CO₂ _(L) and the said gas into the liquid underpressure. Advantageously, as already mentioned, the said injection headhas at least two inlets and one outlet. Particularly advantageously ithas, facing the injector, a first inlet for the CO₂ _(L) , facing thesaid first inlet a (direct) outlet into the liquid and, arranged at 90°from its axis connecting the said first inlet and the said outlet, asecond inlet for the gas.

The injection head of the injection device according to the invention istherefore connected firstly to a suitable source of CO₂ _(L) andsecondly to a suitable source of protective gas.

Insofar as it has been seen that the said protective gas may consist ofCO₂ _(G) and advantageously that the said CO₂ _(G) comes from vaporizinga fraction of the CO₂ _(L) tapped from the CO₂ _(L) supply circuitsupplying the injection valve, it will be understood that according toan advantageous alternative form, the injection device comprises,arranged on the said CO₂ _(L) supply circuit, upstream of the injectionvalve, means for tapping and vaporizing a fraction of the said CO₂ _(L); the said tapping and vaporizing means being connected to the means forsupplying the injection head with gas. The, safeguarded CO₂ _(L)injection device according to the invention can therefore operateconnected to just one source of CO₂ _(L) .

The said device comprises the essential means specified hereinabove,obviously associated with appropriate control means. The said essentialmeans are also advantageously associated with:

means for removing the gas delivered into the liquid and, according to aparticularly advantageous alternative form, means for recycling the saidrecovered removed gas. In the particular context where the injectionhead of the injection device according to the invention is tapped intothe wall of a pipe inside which the liquid circulates under pressureunder the action of means (such as pumps) for circulating under pressurethe said liquid, the said means for removing the gas delivered into thesaid pipe are obviously arranged downstream of the said injection headand are advantageously slaved to the said means for circulating the saidliquid under pressure so that removal of the said gas is performedwithout any effect on the circulation of the said liquid. In any event,it is within the competence of the person skilled in the art to designsuch means of removing the gas delivered to the chamber and possibly ofcoupling the said removal means to means for recycling the saidrecovered delivered gas;

a device for controlling the temperature of the liquid into which theCO₂ _(L) is injected. The intervention of such a control device isbeneficial, for obvious safety reasons. This control deviceadvantageously comprises means for measuring the temperature of the“treated” liquid and means for stopping the injection of the CO₂ _(L) ;the means are to be actuated when the said temperature is below areference temperature. It will be understood that, in a particularlyadvantageous manner, the said device also comprises means forautomatically controlling the said means for stopping the injection ofCO₂ _(L) which automatic-control means automatically activate the saidstopping means as soon as the measured temperature is below a referencevalue. With or without the intervention of such automatic-control means(advantageously with) it is strongly recommended that the means ofstopping the injection of the CO₂ _(L) comprise a so-called safetyvalve, mounted on the CO₂ _(L) supply circuit upstream of the CO₂ _(L)injection valve. This then yields a device for controlling thetemperature which independently of the regulation provides theinstallation with positive temperature protection (because the safetyvalve or shut-off valve is upstream of the injection valve).

The present invention, in both its method and device aspects, is nowdescribed with reference to the single appended figure. The said figurediagrammatically depicts a device of the invention which is suited toimplementing an advantageous alternative form of the method of theinvention.

Liquid carbon dioxide (CO₂ _(L) ) from a source S is injected accordingto the invention—under the protection of a stream of carbon dioxide gas(CO₂ _(G) ) when injection is stopped—into a liquid effluent Lcirculated under pressure by means of the pump P in the pipe C. The saidinjection of CO₂ _(L) is at fixed flow rate, and is regulated in steppedmode.

It is implemented slaved to automatic-control means 2, to regulate thepH of the said liquid effluent The means 1 of injecting the said CO₂_(L) into the liquid effluent L mainly consist of an injection valve 1a, of the ball valve type, connected directly to an injection head 1 btapped into the pipe C. The said valve 1 a is equipped with an injectori, on the injection head 1 b side. The said injection valve 1 a operatesin all or nothing mode; it is either open or closed. Its opening and itsclosure are controlled by the actuator 1 c, slaved to theautomatic-control means 2. The said actuator 1 c, located at somedistance in a temperate zone, is supplied with gas via the CO₂ _(G)supply circuit, to cause it to work.

The said valve 1 a is open when the pH of the liquid effluent L is abovea preset reference value; it is closed by the actuator 1 c when the saidpH remains below or equal to the said reference value. The said valve 1a is supplied with CO₂ _(L) via the supply circuit 3 connected to thesource S.

The injection head 1 b tapped into the pipe C makes it possible,alternately, to deliver CO₂ _(L) and CO₂ _(G) into the liquid effluentL. It comprises:

facing the injector i of the valve 1 a, a first inlet of CO₂ _(L) ;

facing the said first inlet, an outlet (into the liquid effluent L),

and, arranged at 90° to its axis connecting the said first inlet and thesaid outlet, a second inlet for the CO₂ _(G) .

A line 6 for carbon dioxide in the gaseous state (CO₂ _(G) ) permanentlysupplies this second inlet via, in this order, a serpentine coil 7, apressure reducer 5, a flow-regulation valve 6 a and, finally, anon-return valve 6 b. In the context of the alternative form depicted,the protective gas used is therefore carbon dioxide tapped from theliquid carbon dioxide supply circuit 3. The fraction of CO₂ _(L) tappedoff is heated and vaporized in the said serpentine coil 7, at ambienttemperature. It is then expanded by the pressure. reducer 5 before beinginjected via the flow-regulation valve 6 a, the non-return valve 6 b andthe injection head 1 b.

The pipe C is fitted, downstream of the injection head 1 b, with means4, for removing the injected CO₂ _(G) . The said removal means 4comprise:

a vent valve 4 a,

an actuator 4 b which brings about the closure of the said valve 4 a,via automatic-control means 4 c.

The said vent valve 4 a is normally open when power is not applied(always open). Thus, in the event of a power failure, it automaticallyallows the protective CO₂ _(G) to escape. It closes, under the action ofthe actuator 4 b, as soon as the pump P for transferring the liquideffluent L starts to operate. By contrast, as soon as the said pump Pstops, the said valve 4 a opens, thus venting the injected CO₂ _(G) ,thereby preventing the formation of pockets of gas downstream of theinjection. This valve 4 a therefore makes it possible always to keep aliquid charge downstream of the pump P. The said pump P can thereforerestart without the risk of losing its prime.

The device depicted also comprises a unit for monitoring the temperatureof the liquid effluent L. This is because if the period during which theCO₂ _(L) is injected is abnormally extended (for example in the event offailure of the pH meter, failure of the pH regulator, failure of theinjection valve 1 a), the temperature of the said liquid effluent L candrop dangerously, until the pipe C ices up with dry ice.

The said temperature-monitoring unit comprises:

a temperature probe 8, measuring the temperature of the said liquideffluent L;

a device for controlling this temperature, which itself comprisesautomatic-control means 10 and a valve actuator 9 b;

a so-called safety valve 9 a, operated by the said actuator 9 b,arranged on the CO₂ _(L) supply circuit 3 and allowing the CO₂ _(L)supply to be shut off.

The said valve 9 a and its actuator 9 b constitute the means 9 ofstopping the said CO₂ _(L) supply.

This monitoring unit provides positive temperature protection which isindependent of the pH regulation because the safety valve 9 a (orshut-off valve) is upstream of the injection valve 1 a. It will also benoted that the said safety valve 9 a is obviously downstream of thepoint at which the fraction of CO₂ _(L) which is intended, in theserpentine coil 7, to generate the CO₂ _(G) used for regulation,according to the invention, is tapped.

Between the said safety valve 9 a and the injection valve 1 a there is asafety valve 11.

It will also be noted that the actuators involved—the actuators 1 c, 4 band 9 b for actuating the injection valve 1 a, the vent valve 4 a andthe safety valve 9 a, respectively, —are pneumatic actuators suppliedwith gas in the form of CO₂ _(G) tapped from the supply circuit 6 of theinjection head 1 b.

From an examination of the said figure and from the descriptionhereinabove, the person skilled in the art will have fully grasped thebenefit of the present invention which proposes an injection of CO₂ _(L), at a fixed flow rate in stepped mode under the protection of a streamof CO₂ _(G) when injection is stopped. Specifically:

while the CO₂ _(L) is being injected into the liquid effluent L, thesupply of CO₂ _(G) is automatically interrupted by virtue of thepressure differential;

by contrast, as soon as the said injection of CO₂ _(L) stops, the supplyof CO₂ _(G) resumes instantly with a minimal set flow rate, thusthermally insulating the downstream end of the injection zone (which isat about −80° C.) from the liquid effluent L (which itself is at apositive temperature).

The following are advantageously associated with the means necessary forcarrying out the said injection of CO₂ _(L) under CO₂ _(G) protection:

a subassembly for venting the stream of CO₂ _(G) gas;

a subassembly for controlling the temperature of the liquid effluent L.

The present invention is finally illustrated via the example below.

An installation of the type of the one depicted in the appended figureis used under the following conditions.

The liquid industrial effluent which is “to be treated” is transferredat varying flow rates (from 30 to 50 m³/h) using a pump at 2.5 bar froman upstream basin to a downstream basin which empties into the drain.However, the said effluent can be discharged into the said drain only ifits mean pH is a maximum of 8.

A stainless steel sleeve with a nominal diameter of 125 mm, fitted withan injection valve (ball valve+injector at the valve outlet) and with aninjection head, is placed (tapped into the pipe) just after the transferpump so that the CO₂ _(L) injected/treated effluent contact time is aslong as possible, between the two basins.

The injection valve is equipped with a 0.9 mm injector which provides aflow rate of 12 g of CO₂ _(L) per second.

The flow rate of gas protecting the injection head (CO₂ _(G) tapped fromthe CO₂ _(L) supply circuit) has been set to a minimum value of about 3l/min.

A soon as the pH measurement indicates that the effluent has a pH higherthan 8, CO₂ _(L) is injected for a period of the order of 6 seconds outof a fixed 8-second cycle. The length of the injection period decreasesthereafter until it fades to nothing by virtue of the PID loop (whichprovides Proportional Integral Derivative regulation).

What is claimed is:
 1. Method for the regulated injection of liquidcarbon dioxide (CO₂ _(L) ) into a liquid (L) under pressure inside achamber, which comprises: injecting the liquid carbon dioxide (CO₂ _(L)) at a fixed flow rate, in stepped mode, by an injection devicecomprising an injection valve and an injection head tapped into a wallof the chamber, the injection head being positioned directly at theoutlet from the injection valve; and, as soon as each injection ofliquid carbon dioxide (CO₂ _(L) ) stops, a gas is delivered into theliquid (L) through the injection head in place of the liquid carbondioxide (CO₂ _(L) ); the gas being delivered at sufficient pressure toprevent any of the liquid (L) from running back into the injection head.2. Method according to claim 1, wherein the gas delivered is carbondioxide; the carbon dioxide being the result of vaporization of afraction of the liquid carbon dioxide (CO₂ _(L) ) tapped from a liquidcarbon dioxide (CO₂ _(L) ) supply circuit upstream of the injectiondevice.
 3. Method according to claim 1, wherein the gas delivered intothe liquid (L) is at least partially removed and recycled.
 4. Methodaccording to claim 1, wherein the liquid carbon dioxide (CO₂ _(L) ) isinjected at an upstream pressure of between about 14×10⁵ and 20×10⁵ Pa(14 to 20 bar) and at an upstream temperature of between −20° C. and−30° C.
 5. Method according to claim 1, wherein the temperature of theliquid (L) is controlled; the injection of liquid carbon dioxide (CO₂_(L) ) being stopped as soon as the temperature of the liquid (L) isbelow a reference temperature.
 6. Method according to claim 1, furthercomprising regulated injection, in stepped mode, of liquid carbondioxide (CO₂ _(L) ) into a liquid (L) circulating under pressure througha pipe; the gas delivered into the liquid (L), as soon as each injectionof liquid carbon dioxide (CO₂ _(L) ) stops, being at least partiallyremoved when the circulation of the liquid (L) stops.
 7. Methodaccording to claim 1, wherein the liquid carbon dioxide (CO₂ _(L) ) isinjected for descaling purposes and/or for preventing build-up of scale.8. Method according to claim 2, wherein the gas delivered into theliquid (L) is at least partially removed and recycled.
 9. Methodaccording to claim 2, wherein the liquid carbon dioxide (CO₂ _(L) ) isinjected at an upstream pressure of between about 14×10⁵ and 20×10⁵ Pa(14 to 20 bar) and at an upstream temperature of between −20° C. and−30° C.
 10. Method according to claim 3, wherein the liquid carbondioxide (CO₂ _(L) ) is injected at an upstream pressure of between about14×10⁵ and 20×10⁵ Pa (14 to 20 bar) and at an upstream temperature ofbetween −20° C. and −30° C.
 11. Method according to claim 2, wherein thetemperature of the liquid (L) is controlled; the injection of liquidcarbon dioxide (CO₂ _(L) ) being stopped as soon as the temperature ofthe liquid (L) is below a reference temperature.
 12. Method according toclaim 3, wherein the temperature of the liquid (L) is controlled; theinjection of liquid carbon dioxide (CO₂ _(L) ) being stopped as soon asthe temperature of the liquid (L) is below a reference temperature. 13.Method according to claim 4, wherein the temperature of the liquid (L)is controlled; the injection of liquid carbon dioxide (CO₂ _(L) ) beingstopped as soon as the temperature of the liquid (L) is below areference temperature.
 14. Method according to claim 2, furthercomprising regulated injection, in stepped mode, of liquid carbondioxide (CO₂ _(L) ) into a liquid (L) circulating under pressure througha pipe; the gas delivered into the liquid (L), as soon as each injectionof liquid carbon dioxide (CO₂ _(L) ) stops, being at least partiallyremoved when the circulation of the liquid (L) stops.
 15. Methodaccording to claim 3, further comprising regulated injection, in steppedmode, of liquid carbon dioxide (CO₂ _(L) ) into a liquid (L) circulatingunder pressure through a pipe; the gas delivered into the liquid (L), assoon as each injection of liquid carbon dioxide (CO₂ _(L) ) stops, beingat least partially removed when the circulation of the liquid (L) stops.16. Method according to claim 4, further comprising regulated injection,in stepped mode, of liquid carbon dioxide (CO₂ _(L) ) into a liquid (L)circulating under pressure through a pipe; the gas delivered into theliquid (L), as soon as each injection of liquid carbon dioxide (CO₂ _(L)) stops, being at least partially removed when the circulation of theliquid (L) stops.
 17. Method according to claim 2, wherein the liquidcarbon dioxide (CO₂ _(L) ) is injected for descaling purposes and/or forpreventing build-up of scale.
 18. Method according to claim 3, whereinthe liquid carbon dioxide (CO₂ _(L) ) is injected for descaling purposesand/or for preventing build-up of scale.
 19. Method according to claim4, wherein the liquid carbon dioxide (CO₂ _(L) ) is injected fordescaling purposes and/or for preventing build-up of scale.